This invention relates generally to an implantable pacing lead for use with a cardiac pacemaker, and more specifically, to a pacing lead having lead body wherein the conductors are protected from being crushed by the subclavian bone and muscle structure.
Clinical evidence suggests that certain upper extremity activities are contraindicated for persons with permanent pacemakers because they require movements that can cause damage to leads. Currently, leads used in cardiac stimulation are often implanted transvenously or transthoracically with the result that the lead body can be physically crushed by either bones (i.e. "first rib-clavicle") or by tissue (costoclavicular ligament complex, subclavius muscle) and by anchoring sleeves which are tied-down so tightly that the lead body can be crushed or damaged. The result of these crushing or constrictive stresses can be severe damage to the conductors within the lead body which, in turn, can result in failed conductors and/or failed insulation.
Some leads and central venous catheters placed by percutaneous subclavian venipuncture have developed a number or problems that are apparently associated with the costoclavicular region near the superior thoracic aperture. Catheters or leads implanted by subclavian venipuncture can be damaged by bony compression or impingement by dense tissues as the lead passes through the vein beneath the clavicle, over the first rib, and into the thorax just lateral to the sternoclavicular joint. Studies suggest that an overriding clavicle can crush leads against the first rib with a "pincherlike" action. Leads can also be compressed within the costoclavicular ligament complex.
Conductor mechanical damage including fractures and/or insulation breaks occurs in about 2% to 3% of all implanted leads. In patients who are not pacemaker dependent, the event is usually not life-threatening, but can require invasive corrective procedures with potential complications. Mechanical damage is defined as coil deformation, coil fracture, mechanically induced insulation breeches, and insulation wear observed individually or in combination. Pacing lead coils under compression are characterized by flattened helical conductors. Fatigue fractures resulting from repeated cyclic compressive loading usually initiate at the outer surface of the coil.
A recent study, by Donald M. Jacobs et al., published in Part I of the March 1993 issue of Pace Magazine, documents the mechanisms involved in the compression deformation of implanted leads. The study involved 49 compression damaged leads of one manufacturer. While the study was aimed at identifying causes of lead compression and different implant techniques that avoid causing compression damage to the lead, they identified the site of the damage as being 27.5+/-5.2 centimeters distal to the connector pin on 58 centimeter leads.
In view of the foregoing, it has been proposed that the percutaneous subclavian venipuncture approach should be abandoned because the incidence of lead fracture in the costoclavicular region is unacceptable. However, it is also recognized that this method of implant has become the standard procedure for the majority of pacemaker lead implants. Accordingly, it would be beneficial to have a lead design which resists rib-clavicle, tissue and suture sleeve imposed mechanical damage, and allows continuation of accepted implanting procedures.